Metallurgy



Dec. 10, 1935.

FREDERICK LAIST ATT ORNE Yi Patented Dec. '10, 1935 UNITED STATI-:s

PATENT. ori-ICE Anaconda Copper Mining Company, New York,

N. Y., a corporation of Montana Application January 5, 1934, Serial No. 705,335

, Claims. This invention relates to metallurgy and has @for an object the provision of an improved metallurgical process. More particularly, ,the invention contemplates the provision of an improved v'process for the treatment of copper-base alloys containing zinc.

Alloy scrap such as brass and bronze scrap containing copper, zinc, lead and tin isavailable in such quantities' as to provide a source of these elements of considerable importance in view of prevailing economic conditions. Various procedures for separating and recovering the components of the scrap have been proposed and employed heretofore. Such procedures, however, have been ineiilcient and expensive to carry out. Thus, for example, it has been proposed heretofore to subject the alloy in the form of a molten bath to an oxidizing treatment to eect the elimination of zinc, lead andl tin as oxide fume and/or slag. This procedure contemplated'further treatment of the metallic copper and the oxides for the separation and' recovery of pure metallic products. It has been found, however,

that the complete elimination of zinc, lead and tin by means of an oxidizing treatment is dilcult and expensive and that the separation and recovery of zinc, leadand tin from the oxide products presents many difiiculties. I

It has also been proposed to treat the alloy by electrolysis, after casting into 'suitable anode form, to produce a deposit of metallic copper. According to the procedures of this type proposed heretofore, deposition of copper by electrolysis is continued until the amount of zinc in the electrolyte reaches certainvpredetermined proportions.

The electrolyte is then treated for the recovery of its zinc content. This type of procedure has been employed somewhat more successfully than the procedure involving the elimination` of lzinc, lead and tin by means of an oxidizingtreatment, but it has-been found to be quite expensive when carried out to the point at which copper and zinc products of suitable commercial purity are produced.

The present invention provides an ,effectiveY and relatively inexpensive method for recovering high-grade metallic copper and zinc products from copper-base alloys containing zinc. During the course ofthe process, other components of the alloy such as lead and tin are obtained in such forms that they may be readily separated and recovered.

According` to the process of the invention, an anode of theA alloy is electrolyzed in an electro- (cl. 20a-57) lyte containing copper and zinc sulphate to produce av deposit of metallic copper.

I'he anodes employed may vary widely in composition. Following is a typical analysis of anode metal; Cu 82%, Zn 12%, Pb 3%, Sn 3%. The 5 electrolyte employed preferably contains several times as much zinc as copper. A preferred type of electrolyte may contain about 120 grams per liter of zinc and about 30 grams per liter of coplo per.

During the course of the electrolytic treatment, the electrolyte tends to become depleted in copper and enriched in zinc. Consequently, copper must be incorporated in the electrolyte from some convenient source and zinc must be removed from I the electrolyte in order that the electrolytic process may operate effectively. Adjustment of the copper and zinc contents of the electrolyte may be made intermittently, as required in order to maintain .a suitable degree of eiliciency, or continuouslyy in such a manner as to maintain in the electrolytic cells, an electrolyte of substantially constant composition.

Forthel purpose of adiusting the composition of the electrolyte and recovering zinc contained therein, a portion of the electrolyte is withdrawn intermittently or continuously and treated with one or more agents capable of effecting the precipitation of copper contained therein. The resultinglsbstantially copper-free solutionis-treated electrolytically to obtain metallic zinc.

According to the preferred process of the lnvention, the electrolyte is withdrawn continuously from the copper cells, and adjustment of the copper and zinc contents ofthe electrolyte is carried out continuously in order to maintain the composition of the electrolyte substantially constant. The electrolyte withdrawn from the copper cells is treated with one or more agents'such aszihc oxide and calcium carbonate to neutralize the 40 acid contained therein and precipitate the major portion of the copper. The resulting partla'liy purified, neutral zinc `sulphate solution is then treated with an agent such as zinc dust to preper sulphate solution which is returned to the copper cells for adjusting the'composition of the electrolyte. 'I'he spent electrolyte may be passed in contact with the copper precipitate or employed in any suitable manner to extract the copper contained in the precipitate. Additional copper or acid required for restoring the copper electrolyte may be obtained from any suitablesource.

Such iron as the anodes contain will dissolve .together with zinc in the copper electrolyte. The accumulation of iron in the bath is apt to assume troublesome proportions unless it is continually removed at some step in the procs. This step is provided by the treatment with zinc oxide (ZnO) which precipitates not only copper but iron as well. In order to insure complete precipitation of the iron, it is preferably first oxidized by means of MnOz or other suitable oxidizing agent. Antimony and arsenic, if present, will be precipitated with the iron. When redissolving the precipitated copper hydroxide (Cu(OH)) with acid from the zinc cells, the iron, antimony and arsenic may for the most part be left behind by keeping down the acid concentration.

According to the preferred complete process of the invention, zinc oxide for use in precipitating copper from the electrolyte withdrawn from the copper cells is obtained by oxidation of the alloy to be treated for the recovery of its components. Virtually all processes for the treatment of copper-base alloys by electrolysis require the melting of the raw material in order that anodes of suitable shapes may be formed. The present invention utilizes a blowing treatment during the melting operation to accomplish the double purpose of providing a source of heat for aiding in the melting through oxidation of the zinc, and a reagent for subsequent use in promoting the separation of the copper and zinc.

The invention will be better understood from a consideration of the following description and the accompanying flowsheet illustrating a preferred complete process of the invention.

Scrap alloy metal analyzing 74% copper, 20% zinc and approximately 3% lead and 3% tin is melted in a reverberatory furnace and the bath is agitated by means of air under pressure introduced through suitable pipes. While it is dimcult to eliminate all of the zinc by blowing with air, about 40% to 50% may be fumed off as oxide quite readily, and the zinc oxide (ZnO) fume thus produced is comparatively free from other substances. Lead and tin will practically all remain in the bath. Blowing of the molten bath is continued until about 40% to 50% of the zinc has been oxidized and driven off in the form of a fume which is collected in bag filters for subsequent use in the process. 'Ihe remainder of the molten alloy, modified by the removal of a portion of its zinc content, is cast into anodes which will have approximately the following composition, if it is assumed that about 40% of the zinc has been fumed off; Cu 82%, Zn 12%, Pb 3% and Sn 3%.

These anodes are now immersed in a bath an-A alyzing approximately 30 grams per liter'icopper and 120 grams per liter zinc as sulphates, together with 50 lgrains per liter of sulphuric acid.

K 'lhere may be substantial variations from these proportions, but it is important to the economy of the process that the percentage of zinc be high in relation to that oi' copper and/or acid. The electrolyte should contain as much z'lnc as possible without becoming viscous, and the copper tutti` `liberated at the anodes.

acid should be as low as possible while still providing for satisfactory deposits of copper on the cathodes and a bathof reasonably low electrical resistance. 'I'he electrolysis is carried on as is customary in electrolytic refineries for blister copper except that provision must be made for the removal of a greater quantity of slimes" since the leadand tin of the alloy accumulate in these. 'I'he lead and tin may be recovered from the slimes by well known methods, and, at the same time, any copper which may be present in the slimes may be recovered and returned to the electrolytic circuit.

As the electrolysis proceeds, the anodes corrode as the copper and zinc contained therein combine with the S04 ions liberated thereon to form soluble sulphates, and the lead and tin are converted into insoluble compounds. At the same time copper is deposited on the cathodes in in amount chemically equivalent to the S04 ions Therefore, when electrolyzing anodes of the composition assumed herein, more copper will be deposited at the cathodes than is dissolved at the anodes, and the excess must come out of the electrolyte which becomes impoverished in copper. 'I'his loss may be made up in any suitable manner as, for example, by dissolving copper-bearing substances such as copper oxide, scrap copper, cement copper and copper sulphate in the electrolyte. The addition of copper sulphate will restore not only the copper strength of the bath but also the acid strength which tends to decrease due to combination of the S04 ions with zinc, lead and tin. For the purpose of incorporating copper in the electrolyte, the main body of electrolyte from the, cells may be circulated in contact with the copper-bearing substances, the enriched electrolyte being returned to the cells. Copper may beincorporated in the electrolyte in any other suitable manner as well.

While the electrolyte tends to become impoverished in copper, it tends to become enriched in zinc. In order to avoid excessive concentration oi' zinc and to provide for the separation and recovery of the zinc dissolved from the anodes, a portion of the copper electrolyte is continually withdrawn and replaced with 'a' corresponding amount of solution from which the'zinc has been partially removed.

The solution withdrawn from the copper circuit may be assumed to have the following approximate analysis: Copper 30 grams per liter, zinc 120 grams per liter, sulphuric acid 50 grams per liter. It is to be electrolyzed for the recovery of its zinc content, but before this is done, it should be neutralized, the coppershould be re-4 moved, and it must be completely purged of objectionable impurities. Neutralization of the acid of the withdrawn electrolyte is accomplished by adding thereto an amount of zinc oxide `(Zn)' suflicient for that purpose, preferably fumel collected from the anode furnace and produced during the blowing treatment. The neutralization proceeds rapidly and with evolution of heat.

Additional ZnO is now added with constant agitation for the purpose of precipitating copper, chiefly as Cu(OH) z, which comes down as a ilocculent, easily filter-able precipitate. Some basic copper sulphate may come down at the same time. I! the temperature is maintained above 40 C., and if an hour or more of time is allowed for the reaction to proceed, approximately 95% of the copper may be precipitated with the theoretical amount of zinc oxide (ZnO) After nlteringoil' this precipitate the solution is subjected to well known standard methods of purification, and the puried solution is electrolyzed for the recovery of metallic zinc. 'I'he treatment with zinc oxide (ZnO) has, of course, resulted in raising the zinc content of the solution which now analyzes approximatelyz-Zinc 180 grams per liter, copper 2 grams per liter, acid nil. After purification with zinc dust, the copper content becomes nil.

` The spent electrolyte from the zinc cells runs about 20 grams per liter zinc, and the acid has increased to about 240 grams per liter. The solution is now used to re-dissolve the copper hydroxide precipitate which resulted from the addition of zinc oxide (ZnO) to the neutralized electrolyte from the copper circuit, thus restoring this copper to the circuit. The solution, depleted in zinc, is now returned to the copper bath from which it was taken. This returned solution analyzes approximately as follows: Zinc 20 grams per liter, copper 30 grams per liter, sulphuric acid 195 grams per liter.

p 1. The method of treating an alloy containing copper and zinc to obtain separate copper and zinc products which comprises subjecting the alloy in the form of a molten bath to a blowing treatment to recover a portion of its zinc content as zinc oxide, subjecting the thus modiiied alloy to an electrolytic treatment in an electrolyte containing sulphuric acid and sulphates of zinc and copper to produce a metallic copper product and to convert the zinc of the alloy to zinc sulphate which dissolves in the electrolyte, treating the resulting electrolyte with one or more agents including zinc oxide obtained in the blowing treatment to neutralize the acid and precipitate the copper contained therein, thereby to produce a neutral, substantially copper-free4 solution of zinc sulphate, treating the thus puriiied zinc sulphate solution electrolytically to recover metallic zinc, and utilizing the resulting impoverished solution to produce electrolyte for the electrolytic treatment of the alloy.

2. The method of treating an alloy containing copper and zinc to obtain separate copper and zinc products which comprises subjecting the alloy to an electrolytic treatment in an electrolyte containing sulphuric acid and sulphates of zinc and copper to produce a metallic copper product and to convert the zinc of the alloy to zinc sulphate which dissolves in the electrolyte, treating the resulting electrolyte with one or more agents including zinc oxide to neutralize the acid and precipitate the copper contained therein, thereby to produce a neutral, substantially copper-free solution of -zinc sulphate, treating the phate, and utilizing the resulting solution to pro-` duce electrolyte for the electrolytic treament of the alloy.

3. The method of treating an alloy containing copper and zinc to obtain separate copper and zinc products which comprises subjecting the alloy to an electrolytic treatment in an electrolyte containing sulphuric acid and sulphates of zinc and copper to produce a metallic copper prod- 5 uct and to convert the zinc of the alloy to zinc sulphate which dissolves in the electrolyte, treating the resulting electrolyte with one or more agents including calcium carbonate to neutralize the acid and precipitate the copper contained 10 therein, thereby to produce a neutral, substantially copper-free solution of zinc sulphate, treating the thus purified zinc sulphate solution electrolytically to recover metallic zinc, passing the resulting impoverished solution having a relatively l5 high acid content in contact with the copper precipitate to form a solution containing copper sulphate, and utilizing the resulting solution to produce electrolyte for the electrolytic treatment of the alloy.

4. The method of treating an alloy containing copper and zinc to obtain separate copper and zinc products which comprises subjectingthe alloy in the form of a molten bath to a blowing treatment to recover a portion of its zinc content 25 as zinc oxide, subjecting the thus modified alloy to an electrolytic treatment in an electrolyte containing sulphuric acid and sulphates of zinc and copper to produce a metallic copper product and to convert the zinc of the alloy to zinc sulphate 30 which dissolves in the electrolyte, treating the resulting electrolyte with one or more agents including zinc oxide obtained in the blowing treatment to neutralize the acid and precipitate the copper contained therein, thereby to produce a 35 neutral, substantially copper-free solution of zinc sulphate, treating the thus puried zinc sulphate solution electrolytically to recover metallic zinc, passing the resulting impoverished solution in contact with the copper precipitate to form a 40 solution containing copper sulphate, and utilizing the resulting solution to produce electrolyte for the electrolytic treatment of the alloy. l

5. 'Ihe method of treating an alloy containing copper and zinc to obtain separate copper and 45 zinc products which comprises subjecting the alloy to an electrolytic treatment in an electrolyte containing sulphuric acid and sulphates of zinc and copper to produce a metallic copper product and to convert the zinc of the alloy to zinc sulphate which dissolves in the electrolyte, treating the resulting electrolyte with two or more agents including zinc oxide and zinc dust to neutralize the acid and precipitate the copper and other impurities contained therein, thereby to 55 produce a neutral, substantially copper-free solution of zinc sulphate, treating the thus purlled zinc sulphate solution electrolytically to recover metallic zinc, passing the resulting impoverished solution having a relatively high acid content in contact with the copper precipitate to form a solution containing copper sulphate, and utilizing the resulting solution to produce electrolyte for the electrolytic treament of the alloy.

FREDERICK LAIsT. 

